This invention pertains to the field of membrane-type filter devices, particularly intravenous filter devices which employ both hydrophilic and hydrophobic membranes.
This invention relates broadly to membrane-type filter devices, and especially to filter devices used to remove impurities from liquids or fluids that are to be introduced intravenously to the human body. Some fluids useful with this invention include saline solutions and nutrient solutions, or other solutions that act as carriers for drugs. Other fluids useful with this invention are not listed but are well known to those having ordinary skill in the art.
One of the problems encountered with conventional membrane-type intravenous filter devices is the presence of gas. The fluid must be filtered before entering the patient in order to remove gas bubbles and contaminants. Gas in the housing or mixed with the liquid tends to prevent effective filtration of the liquid. When the filter is first attached to the patient and fluid flow is initiated, air frequently enters the lines or is already present in the filter device. A wetted hydrophilic membrane filter will generally not allow the air to pass. Thus, entrapped air tends to prevent fluid from entering the patient. It is therefore desirable to remove this entrapped air as quickly and continuously as possible. This is often referred to as priming the filter.
Several options are available to remove air from membrane-type filter devices. Many of these options make use of hydrophobic membranes which are capable of passing air out of the filter housing through vents, but liquids will not pass through the membranes. Conventional intravenous filters employ this principle but have some shortcomings. For example, several commercial devices are not altogether satisfactory because they do not remove air through the outlet port in the short time that is necessary, or they require the filter to be turned upside down, or in an orientation different than how the filter will be used, during priming. This can lead to confusion and a lack of proper priming, leaving gas entrapped in areas of the housing that are not contiguous to the hydrophobic membrane.
Various ideas have been used in an attempt to correct these shortcomings. Some manufactures utilize rectangular filters to assist self-priming, with an inlet at the bottom and an outlet at the top of the filter. Such devices must be tilted from a horizontal plane in order to be self-priming. Some do not utilize a hydrophobic-type filter medium. Still other filter units employ a combination of hydrophilic and hydrophobic filters arranged side-by-side in alternate sequence. A disadvantage, however, is that this configuration provides a hydrophobic zone on each end of the housing. Although these chambers appear to provide for the escape of entrapped air, they also create a zone where liquids can gather and be incapable of passing through either the hydrophilic membrane or the hydrophobic membrane. Further, drugs in intravenous fluids often have different densities than other fluids administered to the patient. This may mean that the drugs will be in a portion of the filter adjacent a hydrophobic membrane if the filter unit is in a vertical position. When this is the case, the drugs may not immediately be administered to the patient. This could conceivably cause problems, especially if drugs must be administered quickly to the patient.
One product, known as the Gelman IV-4 filter, has two vent holes on the back side so as to allow venting from two places in the inlet chamber. However, there are increased manufacturing costs from having to seal two hydrophobic membranes while constructing the filter, plus this design doubles the possibility of a defective filter due to a leak if the hydrophobic material is not correctly sealed.
Another problem is that support ribs, used to hold the filtration media away from the wall of the filter housing, create many small flow channels. Small bubbles can form in these channels during priming and, even though the filter is properly oriented, the bubbles may stay trapped in the narrow ends of the channels and not be flushed out the outlet port.
An additional problem is that many filters have tubing connections that orient the filter in such a manner that if the filter is suspended from an intravenous fluid source, with additional tubing suspended therefrom, the filter either does not hang so that the vent is properly positioned, or the weight of the filter, or tension on the tubing if the patient pulls on the tubing, causes the filter to tip to one side and kink the tubing.
The problems enumerated in the foregoing are not intended to be exhaustive but rather are among many which tend to impair the effectiveness of previously known filter devices. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that filter devices appearing in the art are not altogether satisfactory.
U.S. Pat. No. 5,827,429 discloses an IV filter that overcomes many of the foregoing disadvantages. The commercial embodiment of the inventive filter of the '429 patent has one hydrophobic media with two air vent holes. Both of these holes exit on the front side of the filter under the inlet to the filter where hopefully they would not be blocked if someone taped the filter onto a surface. However, even this design has some room for improvement.